The aim is to determine how action potentials cause contraction in amphibian skeletal muscle. Various voltage-clamp techniques will be used to study: 1) ionic channels contributing to electrical excitability; 2) the potential dependence and kinetics of contractile activation, and 3) the role of dielectric displacement currents in the regulation of contraction. Pharmacological modifications of the excitation-contraction coupling mechanism and of calcium channels will be compared, combining electrical recording and fluoresence microscopy.